Especially for multiband/multistandard capable power amplifier modules, which are e.g. used for software defined radio applications, different frequency bands and standards have to be covered by one single amplifier module, making high demands regarding bandwidth, output power, efficiency, costs, etc.
Currently the realisation of a described power amplifier module covering a very wide bandwidth (e.g. 800 MHz-2.7 GHz) for high output power levels is a main problem. Since the available bandwidth of a power transistor decreases with increased output power, it's very difficult or not realisable to cover the complete mentioned frequency range by a single power transistor for high output power levels.
It is known to use pre- and driver amplifier stages for amplifying signals over the complete frequency range up to medium output power levels. To reach higher output level suitable partitioning of the frequency range can be done. Thus separate power transistors can be used for the final amplifier stage, which have to cover smaller bandwidths. Partitioning of the frequency range is usually done by frequency splitters or non-frequency selective power divider as known from data sheet of Mini-Circuits “Coaxial Power Splitter/Combiner” (www.minicircuits.com). However, known frequency splitters show a very high power loss.
Furthermore it is known to use a stage-bypassing principle to address different standards with different peak-to-average signal-power ratios (PAR) in different frequency bands. For signals which require less peak output power the last amplifier stage can be bypassed and switched off.